Vascular tissue in traps of Australian carnivorous bladderworts (Utricularia) of the subgenus Polypompholyx

Utricularia (bladderworts) are rootless carnivorous plants forming small suction traps which are hollow discoid bladders. There is some controversy surrounding the understanding of trap vascularization in Utricularia species and most of the knowledge in the literature is based on aquatic Utricularia from section Utricularia. In this study, we investigated trap vascularization in 9 Utricularia species or clones from the subgenus Polypompholyx using several light microscopy staining techniques. Both xylem and phloem elements were found in the traps of all investigated species or clones. The pattern of trap vascular bundles from the subgenus Polypompholyx was similar to that reported for subgenus Bivalvaria, but different from that of aquatic U. vulgaris from the subgenus Utricularia. The system of trap vascularization in the members of the subgenus Polypompholyx was different from that found in the traps of Genlisea, which is a closely related genus (both Lentibulariaceae). The structure of trap vascular bundles was, however, similar in Genlisea and Polypompholyx. Possible utilization of xylem elements in Utricularia traps is discussed.